Matlab: Using a Variable's value in Another Variables Name?

Question

I am wondering if this is possible. My code looks like this:

indexStop = find(firstinSeq(x,4) ~= littledataPassed(y:length(littledataPassed),4), 1, 'first');
for z= 0:(n-1)
indexProcess = find((littledataPassed(y:y+indexStop-1,6) == 1 & ... 
   littledataPassed(y:y+indexStop-1,2) == firstinSeq(x,2) & ... 
   littledataPassed(y:y+indexStop-1,5) == z), 1, 'first'); 
if isempty(indexProcess)
   msgLength[n](countmsgLength[n],:)= [firstinSeq(x,:) [0 0 0 0 0 0]];
else msgLength[n](countmsgLength[n],:)= [firstinSeq(x,:) littledataPassed(y+indexProcess-1,:)];
end
countmsgLength[n]= countmsgLength[n] + 1;
end

I am hoping to have everywhere that reads [n] be switched to the actual value of n, such that I could use this to add data to nine different variables in the format 'msgLength#.' I have tried searching tutorials and what not but haven't seen anything on the topic.

Thanks!!

Answer 1

It's almost always better to use arrays or cell arrays to store data than to create a bunch of variables named a1, a2, a3, etc. For example, you can initialize msgLength as a cell array with n elements:

msgLength = cell(1,n);

And you can access cells of msgLength using curly braces:

msgLength{n} = ...  %# Assign something to cell n

Your variable countmsgLength can just be a regular numeric array, since it appears to only store n values. You would just have to change the square brackets to parentheses (i.e. [n] to (n)).

However, if you really want to create n separate variables, you will likely end up using the EVAL function. This question and this question show some examples of how to create variables names using the value of another variable.

Answer 2

If you absolutely have to use multiple variables, structure dynamic fieldnames using () notation would be handy. If you enter the following:

>> n = 1;
>> data.(sprintf('msgLength%u', n)) = [1 2 3 4];
>> n = 2;
>> data.(sprintf('msgLength%u', n)) = [5 6 7 8];

You'll get a structure with two fields:

>> data
data = 
   msgLength1: [1 2 3 4]
   msgLength2: [5 6 7 8]

Despite this, I second gnovice's suggestion of using an array to store data instead of several variables. You could simply add another dimension to msgLength so line 7 becomes:

msgLength(n,countmsgLength(n),:)= [firstinSeq(x,:) [0 0 0 0 0 0]];